1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to a tool for measuring features on an integrated circuit or probe card.
2. Description of the Related Art
Diagnostics comprise a vital aspect of integrated design and fabrication. Verification of electrical characteristics of integrated circuits is necessary to confirm not only proper circuit design and performance, but also the accuracy and consistency of semiconductor fabrication processes.
Vertical probing represents one commonly used diagnostic technique. The method utilizes a probe card that often consists of a probe head mounted on a plate and a printed circuit board mounted beneath the plate. The probe head includes an array of vertically disposed pins that are sandwiched between plates or die. The pins may be quite small and number in the thousands. One of the die has a plurality of bores through which the pins respectively project. The pins are designed to slide axially in the bores. However, the pins are curved at one end to prevent them from slipping completely out of the bores. The pins are brought into selective contact with the printed circuit board during probe testing of an integrated circuit.
To perform a probe test, the probe card is positioned so that the pin array faces downward and the pins are suspended. An integrated circuit is then moved upward into contact with the pin array and various signals are propagated to and from the integrated circuit via the pins. The pins are forced upward axially when the integrated circuit contacts the pin array. The contact by the integrated circuit inflicts mechanical stresses on the pins in the form of both physical loads and thermal stresses. Like most mechanical structures subjected to mechanical stresses, the pins exhibit wear and deformations over time. Deformed, badly worn or fractured pins can lead to false probe readings and wasted diagnostic efforts.
Thus, it is desirable to check the condition of the probe card pins on a regular basis in order to avoid erroneous diagnostics. Conventional techniques typically involve optical or mechanical measurement of pin height. In many conventional optical methods, the pin array is positioned in the usual sense, that is, facing downward. Optical instruments on the probe machine are then used to observe the pin heights. In other techniques, the probe head is flipped and pins are observed from overhead. Both types of optical methods are generally non-destructive. However, optically measuring the pins introduces errors in both optics focus, and to some extent, operator error. Accurate optical measurement requires not only precise but also consistent focusing of microscope optics. Furthermore, consistent interpretation of observed height by operators is necessary in order to avoid false readings. Obviously, human imprecision can lead to inaccurate measurements. Finally, if probe card is inverted for traditional inspection, the pins may not extend from the bores uniformly across the array, and thus result in erroneous measurements.
In conventional mechanical measurement, an instrument is brought into contact with one or more of the pins to measure height. A risk associated with this technique is damage to the pins. If the instrument exhibits lateral movement during examination of the pins, shearing forces may plastically deform or even fail one or more of the pins.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a measurement tool is provided that includes a frame that has a first member. A second member is provided that is moveable relative to the first member along a first axis and a second axis. The first and second members have first and second cooperating structures engageable to enable the second member to be moved downward along the second axis to a preselected elevation when the second member is moved to a preselected position along the first axis. The movement of the second member along the first axis is constrained when the second member is moved to the preselected elevation. A meter is coupled to the second member for measuring a height of a feature relative to a reference elevation. The meter has a contact surface that contacts the feature when the second member is moved to the preselected elevation. An upwardly facing surface is positioned substantially at the preselected elevation to enable the second member to be moved into contact with the upwardly facing surface without contacting the feature at which point the meter maybe initially set to the reference elevation.
In accordance with another aspect of the present invention, a measurement tool for measuring a height of features of a probe card is provided. The measurement tool includes a frame adapted to seat over the probe card. The frame has an opening to enable overhead access to the features of the probe card, and a first member with a first cooperating structure. A second member is coupled to the frame and moveable relative the first member along a first axis and a second axis. The second member has a second cooperating structure engageable with the first cooperating structure to enable the second member to be moved downward along the second axis to a preselected elevation when the second member is moved to a preselected position along the first axis. The movement of the second member along the first axis is constrained when the second member is moved to the preselected elevation. A meter is coupled to the second member for measuring a height of a feature relative to a reference elevation. The meter has a contact surface that contacts the feature when the second member is moved to the preselected elevation. A biasing member is provided to bias the second member away from the preselected elevation. An upwardly facing surface is positioned substantially at the preselected elevation to enable the second member to be moved into contact with the upwardly facing surface without contacting the feature at which point the meter may be initially set to the reference elevation.
In accordance with another aspect of the present invention, a measurement tool for measuring a height of a plurality of pins of a probe card is provided. The measure tool includes a frame that is adapted to seat over the probe card. The frame has an opening to enable overhead access to the plurality of pins, and a first member with a first upwardly facing opening. A second member is coupled to the frame and is moveable relative to the first member along a first axis and a second axis. The second member and the opening are sized to enable the second member to be moved downward along the second axis to a preselected elevation when the second member is moved to a preselected position along the first axis. When the second member is moved to the preselected elevation, a portion of the second member is positioned in the opening such that the movement of the second member along the first axis is constrained. A meter is coupled to the second member for measuring a height of the plurality of pins relative to a reference elevation. The meter has a contact surface that contacts the plurality of pins when the second member is moved to the preselected elevation. A biasing member is provided to bias the second member away from the preselected elevation. An upwardly facing surface is positioned substantially at the preselected elevation to enable the second member to be moved into contact with the upwardly facing surface without contacting the feature at which point the meter may be initially set to the reference elevation.